1. Field of the Invention
This invention relates to methods and kits for the identification of susceptibility to chronic obstructive airway diseases or disorders. Specifically, the method involves the detection of at least one allele in an IL-1B haplotype, such as an allele at the IL-1B (+3954) locus, which is indicative of an increased susceptibility to chronic obstructive airway disease such as asthma. Additionally, the method also involves the detection of an allele at the IL-1B (-511) locus, the presence of which is indicative of an increased susceptibility to severe asthma. Also included in the present invention are kits for the methods herein described.
2. Description of the Prior Art
Chronic obstructive lung disease and chronic obstructive airway disease (COAD) are broad terms used to describe not a disease entity, but rather a complex of conditions that have in common airflow limitation or airflow obstruction. COAD includes asthma, emphysema, chronic bronchitis, and chronic bronchiolitis. The sites of airway obstruction in COADs vary from the upper airways to the most peripheral bronchioles. The exact cause of most diseases of the airways is not well understood. The definition of airway diseases add to the confusion. Chronic bronchitis is defined clinically by the chronic presence of cough and sputum production. Emphysema, on the other hand, is defined anatomically, on the basis of the breakdown of lung tissue and the enlargement of the alveolar sacs. COADs all have airway narrowing as a disease parameter and they also share inflammation as a component of the disease process.
Asthma is a chronic lung disease characterized by coughing, chest tightness, shortness of breath, and wheezing due to a reversible obstruction of airflow resulting from inflammation and hyper-responsiveness of the airways. In sensitized individuals, inhalation of allergens may produce inflammation of the airway lining, and precipitate a flare-up of asthma. Asthma may also occur as a result of other inflammatory stimuli, such as respiratory tract infections. Individuals who have become sensitized to specific foods may have severely and possibly life-threatening reactions after ingestion of these substances. Asthma, once thought of as a "simple" hypersensitivity reaction, is now known to be a complex condition with a probable spectrum of causes and contributing factors, with airway inflammation as its central attribute. Pulmonary researchers liken it to arteriosclerosis, in the sense that there are many interactive aspects. Many of the contributing factors are now under intensive study, including the chemical reactions that take place in the asthmatic process; the nature of cell-cell communication, the way information is conveyed from one cell or type of cell to another; and the role, reactive or other, of the epithelium. Allergies contribute to both the incidence and severity of asthmatic symptoms. An allergy (also known as immediate hypersensitivity) is defined as an abnormal sensitivity to a substance which is normally tolerated and generally considered harmless, and for which the triggering event is dose-independent, as opposed to a dose-dependent idiosyncratic reaction to a substance. While all immune responses occur as a result of exposure to foreign substances, allergic reactions are distinct from the protective or enhanced "immunity" conferred by immunizations or natural infection. Only about a quarter of the children with asthma outgrow the condition when their airways reach adult size; for the rest, the condition is a lifelong ordeal. The condition persists, according to a research report published by the American Lung Association, in 85 percent of women and in 72 percent of men. (Journal of Allergy and Clinical Immunology Vol. 96:5 11/96).
There were 4,964 deaths from asthma recorded in 1993 in the United States of America. The incidence of asthma mortality in children doubled from 1980 to 1993. Among persons between the ages of 15 and 24 years, the number of deaths rose from 2.5 cases per million in 1980 to 5.2 cases per million in 1993. In 1993, asthma accounted for 342 deaths and approximately 198,000 hospitalization in persons under 25 years of age.
African-Americans account for 21 percent of deaths due to asthma. African-American children are four times more likely to die of asthma compared with Caucasian children. African-American males between the ages of 15 and 24 have the highest risk of mortality.
The mainstay of recognition of susceptibility and estimation of asthma is the family history and the patient's response to therapy. A positive family history tends to be one of the strongest risk factor associated with asthma. Positive identification though, can be difficult. Asthma may coexist with other conditions such as congenital abnormalities, infectious conditions, and cystic fibrosis. Additional indicators are considered when the history is atypical or the response to good medical management is poor. Physicians with less experience in the management of this disease may treat these symptoms as an infection, not realizing that the underlying cause is asthma.
The recognition of asthma severity in children relies heavily on the parents' observations for clinical clues. Correct identification requires an asthma and allergy specialist who recognizes the uniqueness of childhood asthma. More subtle signs of asthma, such as chest tightness, may be overlooked, or the child does not have the capability to properly identify the signs. Recurrent or constant coughing spells may be the only common observable symptoms of asthma in young children. Demonstration of a favorable clinical response to bronchodilator therapy can help confirm the presence of asthma.
There is a tremendous need for early identification of those who are generally susceptible to asthma. A susceptibility test which, from birth, can be used to screen for enhanced risk for a chronic obstructive airway disease would alert doctors to look for early signs of the disease, especially in children. Because it is a chronic and progressive disease when untreated, appropriate treatment could be administered at the earliest stage.
Advantages in positively identifying enhanced risk for asthma are apparent, especially regarding children. Early detection would reduce the costly, time-consuming process of elimination of factors that have routinely been used to identify enhanced risk of asthma.
Adults whose symptoms appear later in life, will benefit from a positive identification of increased susceptibility that allows the physician to treat them effectively without months of guesswork. Appropriate treatment and lifestyle changes can begin in an efficient manner, controlling the symptoms and keeping a positive check on the patient's needs. As disclosed herein, genetic testing can be used to make this important identification of increased susceptibility, and thereby make possible early intervention. The kind of treatment that a patient receives could also be influenced by a positive finding. Individuals are likely to be genetically predisposed to respond to some, but not all, treatment options. Identification of susceptibility to more severe disease by genetic testing of the IL-1 locus could be very useful in a clinical context, particularly for the prevention of severe asthma episodes by more aggressive therapy, and generally for clinical targeting of biomedical manipulation of the IL-1 system.
Genetic testing (also called genetic screening or genotyping) can be defined broadly as the testing of nucleic acid of a patient in an analytical capacity to determine if a patient contains mutations (or alleles or polymorphisms) that either cause or increase susceptibility to a disease state or are in "linkage disequilibrium" with the gene causing a disease state.
Linkage disequilibrium refers to the tendency of specific alleles to occur together more frequently than would be expected by chance. Alleles at given loci are in equilibrium if the frequency of any particular set of alleles (or haplotype) is the product of their individual population frequencies. The cause of disequilibrium is often unclear. It can be due to selection for certain allele combinations, or to a recent admixture of genetically heterogeneous populations. In addition, in the case of markers that very tightly link to a disease gene, an association of an allele (or a group of linked alleles) with the disease gene is expected if the disease mutation occurred in the recent past, so that sufficient time has not elapsed for equilibrium to be achieved through recombination events in that small chromosomal region.
The early detection of a predisposition to genetic diseases presents the best opportunity for medical intervention. Early genetic identification of risk may improve the prognosis for a patient through supervision and early intervention before the clinically detectable disorder occurs.
In cases where patients with similar symptoms are treated with variable success, sophisticated genetic testing can differentiate individual patients with subtle or undetectable differences and can lead to more suitable individual treatments. Early intervention may involve conventional pharmaceutical agents, non-pharmaceutical treatments and newer methods such as gene therapy or treatment with IL-1 modulators. With the development of genetic testing, it is now possible to identify gene mutations that indicate a propensity to develop disease, even when the disease is of polygenic origin. The number of diseases that can be identified by molecular biological methods continues to grow with increased understanding of the genetic basis of multifactorial disorders (see, e.g., U.S. Pat. Nos. 4,582,788; 5,110,920; 4,801,531; 4,666,828; and 5,268,267).
The IL-1 gene cluster is located on the long arm of human chromosome 2 (2q13) and contains at least the genes for IL-1 (IL1A), IL-1 (IL1B), and the IL-1 receptor antagonist (IL1RN) within a region of 430 Kb (Nicklin, et al., Genomics 19: 382-4 (1994)). The agonist molecules, IL-1 and IL-1, have potent pro-inflammatory activity and are at the head of many inflammatory cascades. Their actions, often via the induction of other cytokines such as IL-6 and IL-8, lead to activation and recruitment of leukocytes into damaged tissue, local production of vasoactive agents, fever response in the brain and the hepatic acute phase response. All three IL-1 molecules bind to type I and to type II IL-1 receptors, but only the type I receptor transduces a signal to the interior of the cell. In contrast, the type II receptor is shed from the cell membrane and acts as a decoy receptor. The receptor antagonist and the type II receptor, therefore, are both anti-inflammatory in their actions.
Inappropriate production of IL-1 appears to play a central role in the pathology of many autoimmune and inflammatory diseases, including rheumatoid arthritis, inflammatory bowel disorder, psoriasis, and others. In addition, there are stable inter-individual differences in the rates of production of IL-1, and some of this variation may be accounted for by genetic differences at IL-1 gene loci (Molvig, et at., Scand. J. Immunol. 27:705-16 (1988); Pociot, et al., Eur. J. Clin. Invest. 22: 396-402 (1992)).Thus, the IL-1 genes are reasonable candidates for determining part of the genetic susceptibility to inflammatory diseases such as chronic obstructive airway disease or asthma, most of which have a multifactorial etiology with a polygenic component.
Certain alleles from the IL-1 gene cluster are known to be associated with particular disease states. For example, IL1RN allele 2 is associated with coronary artery disease, osteoporosis, nephropathy in diabetes mellitus (Blakemore, et al., Hum. Genet. 97(3): 369-74 (1996)), alopecia areata (Cork, et al., J. Invest. Dermatol. 104(5 Supp.): 15S-16S (1995)), Graves disease (Blakemore, et al., J. Clin. Endocrinol. 80(1): 111-5 (1995)), systemic lupus erythematosus (Blakemore, et al., Arthritis Rheum. 37: 1380-85 (1994)), lichen sclerosus (Clay, et al., Hum. Genet. 94: 407-10 (1994)), and ulcerative colitis (Mansfield, et al., Gastroenterol. 106(3): 637-42 (1994)). The IL1B allele 2 from marker +3953 of IL-1B is also associated with psoriasis and insulin dependent diabetes in DR3/4 patients (di Giovine, et al., Cytokine 7: 606 (1995); Pociot, et al., Eur J. Clin. Invest. 22: 396-402 (1992)), and severe periodontal disease (Kornman, et al. J. Clin. Periodon. 24.72 (1997)).
However, in none of these studies or reports has there been described an association between asthma and other chronic obstructive airway diseases and the IL gene cluster such that one could identify increased susceptibility and/or monitor such diseases or disorders. These and other disadvantages of the prior art are overcome by the present invention.